21 Second Timer

About this twenty-one second timer

This twenty-one-second countdown runs entirely in your browser. A short interval that works for stretch holds, rest between sets, or quick tasks. There is nothing to install, nothing to sign up for, and no data is uploaded when you start, pause, or reset.

A twenty-one-second countdown is short by design — long enough to matter, short enough that you can hold your position, hold a breath, or hold your attention until it ends. It is a common building block for HIIT circuits, stretching routines, and breathing exercises.

For interval training, queue up several of these in a row by reloading or using a longer timer. For breath work, let the beep mark the transition between inhale and exhale and focus on the next phase rather than the clock.

How to use this timer

• Press Start (or the spacebar) to begin the countdown.
• Press Pause (or the spacebar again) to hold the current time.
• Press Reset (or the R key) to return to 21:00.
• When the timer ends, a short tone plays. Click, tap, or press any key to stop it.
• Use the sound toggle to mute the alert — your preference is remembered on this device.

Tips for accurate timing

• Keep this tab visible. Modern browsers slow down background tabs to save power, which can delay the end alert.
• On mobile, keep the screen awake or plug the device in for long sessions.
• For anything safety-critical, use your device's built-in system timer rather than a web page.

Related timers: 1 minute timer or 30 second timer.

Looking for a different duration? Browse the TimerZen home page or type any whole-number duration into the URL (for example, /45-minute-timer/, /90-second-timer/, or /2-hour-timer/).

Last reviewed on April 24, 2026.